This sounds reasonable if your use case is squeezing more horsepower out of Node applications and the JavaScript part has already been pushed to its limits.

As someone who's done lots of backend development _in_ node though, I'm not really proficient in C++ enough nor I ever had teams able to maintain such modules.

I'm not criticizing your approach, mind you, it's absolutely understandable, just uncommon for someone to be really proficient at both languages.